This invention relates to the analysis of components of an oil composition. In one of its aspects this invention relates to the extraction of components from an oil composition. In another of its aspects this invention relates more particularly to the determination of the amount of ethylene glycol in motor oil. In still another of its aspects this invention relates to the oxidation of ethylene glycol to form formaldehyde. In still another of its aspects this invention relates to a method for determining the amount of formaldehyde in a composition by spectrophotometric methods.
In one of its concepts this invention relates to a method for converting one chemical compound into another chemical compound for which an advantageous analysis method exists. In a more specific concept the invention relates to quantitative conversion of ethylene glycol to formaldehyde with subsequent quantitative conversion of formaldehyde to a blue dye solution so that the spectrophotometric absorbance of the blue dye solution can be calibrated to the amount of ethylene glycol.
The determination of trace concentrations of ethylene glycol in used motor oil has proved to be a difficult task. Final determination techniques either by gas chromatography or by using chemical methods all require removal of the ethylene glycol from the oil before the final determination. Until recently this required the extraction of fairly large oil samples to determine low concentrations of ethylene glycol.
After extraction of the ethylene glycol from oil, the method most commonly used for determining the concentration of ethylene glycol has been a chemical technique requiring oxidation using periodic acid which is a specific oxidant for compounds with hydroxyl groups on adjacent carbon atoms. Periodic acid oxidation of ethylene glycol results in rupture of carbon-carbon bonds to form formaldehyde. The amount of formaldehyde can then be determined spectrophotometrically as a colored dye after reaction with either chromatropic acid or p-fuchsin. The chromatropic acid technique is highly sensitive, but has the disadvantage of requiring concentrated sulfuric acid as solvent. p-Fuchsin must be decolorized with sulfurous acid prior to use and numerous oxidizing agents will regenerate the color.
Another procedure has recently been developed for determining trace concentrations of formaldehyde. In this method, the formaldehyde is condensed with 3-methyl-2-benzothiozilinone hydrazone (MBH) to form an intensely brilliant blue cationic dye. Initial experiments trying to adapt the formaldehyde-MBH condensation to be used with formaldehyde produced by periodic oxidation of ethylene glycol were unsuccessful due to interference in the condensation reaction by the excess periodate used as ethylene glycol cleaving agent. Potassium periodate in acid solution had been the cleaving agent commonly used, but gave such erratic and inconsistent results that the supposed reaction mechanism for producing the brilliant blue dye came under question. It was then discovered that trisodium paraperiodate, Na.sub.3 H.sub.2 IO.sub.6, could be used as an effective oxidant for ethylene glycol and, at the same time, would not oxidize MBH and thereby interfere with its condensation with formaldehyde.
Experimental determinations of 10 to 100 ppm ethylene glycol in used motor oil had indicated that oxidation to formaldehyde followed by the MBH reaction technique has advantages over the current methods of analysis with respect to sensitivity and simplicity. This provides not only an accurate laboratory method for determining ethylene glycol in used motor oil, but also provides a test simple enough to be used in service stations and garages to determine whether there is ethylene glycol in a sample of motor oil from an automobile. The service station and garage testing will become of greater importance as recommendations for using automotive motor lubricants for up to 10,000 miles become more common.
It is therefore an object of this invention to provide a method for determining the presence of ethylene glycol in used motor oil in a range of about 10 to about 100 ppm. It is another object of this invention to provide a sensitive and simply operated method for determining the presence of ethylene glycol in automotive motor lubricants.
Other aspects, objects and the various advantages of this invention will become apparent upon reading this specification and the appended claims.